1. Field of the Invention
The present invention relates to a and, more particularly, to a castor with two braking functions.
2. Description of the Related Art
A conventional castor 1 in accordance with the prior art shown in FIGS. 1 and 2 comprises a castor body 11 provided with an upright shaft 111, a transverse shaft 112, an upper slideway 114, a lower slideway 113 and an arcuate projection 116, a gear 115 connected with a lower end of the upright shaft 111 of the castor body 11 to limit rotation of the upright shaft 111, two rollers 12 mounted on two opposite sides of the castor body 11, a first braking member 13 pivotally connected with the castor body 11 by a pivot shaft 131, a second braking member 14 movably mounted in the lower slideway 113 of the castor body 11 and engaging the gear 115, a sliding block 15 slidably mounted in the upper slideway 114 of the castor body 11, a compression spring 16 mounted in the upper slideway 114 of the castor body 11 and biased between the castor body 11 and the sliding block 15. Each of the rollers 12 has an inner face provided with a plurality of locking grooves 121 arranged in an annular manner. The first braking member 13 has an outer face provided with a pedal portion 132. The first braking member 13 has an upper end provided with a press portion 133 abutting the sliding block 15 and a lower end provided with a push portion 136 abutting the second braking member 14. The first braking member 13 is provided with a first arcuate recess 134, a second arcuate recess 135 and a slot 137. The first arcuate recess 134 and the second arcuate recess 135 of the first braking member 13 are selectively mounted on the arcuate projection 116 of the castor body 11. The second braking member 14 has an outer end connected with the push portion 136 of the first braking member 13 and an inner end releasably engaging the gear 115. The sliding block 15 is provided with a plurality of locking pieces 151 detachably locked in the locking grooves 121 of each of the rollers 12.
In operation, when the pedal portion 132 of the first braking member 13 is pressed downward, the first braking member 13 is pivoted clockwise about the pivot shaft 131 and is moved from the position as shown in FIG. 1 to the position as shown in FIG. 2, so that the push portion 136 of the first braking member 13 drives the second braking member 14 to move inward and to engage the gear 115 so as to lock and prevent rotation of the upright shaft 111. At the same time, the press portion 133 of the first braking member 13 is detached from the sliding block 15, so that the sliding block 15 is pushed outward by the restoring force of the compression spring 16, and the locking pieces 151 of the sliding block 15 are moved and locked in the locking grooves 121 of each of the rollers 12 so as to lock and prevent rotation of the rollers 12. At this time, the second arcuate recess 135 of the first braking member 13 is positioned on the arcuate projection 116 of the castor body 11, and the slot 137 of the first braking member 13 is used to buffer the stress applied on the second arcuate recess 135 of the first braking member 13. On the contrary, when the pedal portion 132 of the first braking member 13 is pulled upward, the first braking member 13 is pivoted counterclockwise about the pivot shaft 131 and is moved from the position as shown in FIG. 2 to the position as shown in FIG. 1, so that the push portion 136 of the first braking member 13 drives the second braking member 14 to move outward and to disengage the gear 115 so as to unlock the upright shaft 111. At the same time, the press portion 133 of the first braking member 13 is moved to press the sliding block 15, so that the sliding block 15 is pressed inward, and the locking pieces 151 of the sliding block 15 are moved and detached from the locking grooves 121 of each of the rollers 12 so as to unlock the rollers 12. At this time, the first arcuate recess 134 of the first braking member 13 is positioned on the arcuate projection 116 of the castor body 11, and the slot 137 of the first braking member 13 is used to buffer the stress applied on the first arcuate recess 134 of the first braking member 13. However, the stress between the castor body 11 and the first braking member 13 is concentrated on the first arcuate recess 134 and the second arcuate recess 135 of the first braking member 13, so that the first arcuate recess 134 and the second arcuate recess 135 of the first braking member 13 are easily worn out during a long-term utilization, thereby decreasing the lifetime of the castor 1.